This book provides a detailed description of the water cycle and the hydrological balance, as well as of the watershed, which is the natural unit for studying all the basic processes related to water. The authors also analyze the specific elements that make up the water cycle: the mechanisms and properties of precipitation, the processes of interception, evaporation and transpiration, infiltration, surface and underground flows and water storage. Next, the book provdes an overview of the various measuring devices available to the hydrologist and the essential methods for acquiring and processing hydrometerological data.